1. Field of the Invention
The present invention relates to a process for producing a high-temperature protective coating for metallic components, in particular components of turbomachines, such as of stationary gas turbines or aircraft engines, which are subjected to thermal loading. Moreover, the present invention relates to corresponding components, in particular of turbomachines, which are subjected to thermal loading and are provided with such a coating.
2. Discussion of Background Information
In the case of components of turbomachines, for example main blade parts, which are exposed to high temperatures, provision is made of suitable coatings in order to protect the base material against hot gas corrosion, for example. In this respect, it is known, for example, to use what are termed MCrAlY alloys as the coating material, where M represents a metal such as nickel, cobalt or a combination of nickel and cobalt, these forming protection against further corrosion at high operating temperatures by virtue of the formation of slowly growing chromium oxide layers or aluminum oxide layers. At temperatures of below 850° C., use is usually made of MCrAlY alloys having a composition which is selected in such a way that, on account of the correspondingly high chromium contents, chromium oxide formation is preferred, this being advantageous particularly in the case of a sulfidation attack. At temperatures of above 850° C., a suitable composition of the coating promotes the aluminum oxide formation, in order to counteract an oxidation attack.
In this context, the so-called MCrAlY layers can additionally be subjected to alitizing in order to promote the aluminum oxide formation by virtue of the additional deposition of aluminum and the thus induced enrichment of aluminum in the coating. However, coatings of this type have a low sulfidation resistance.
Examples of MCrAlY coatings, particularly also for components of turbomachines, are described in DE 28 428 848, EP 2 096 194 A2 and US 2007/0098913 A1, the entire disclosures of which are incorporated by reference herein. However, in the coatings of the prior art, the chromium proportions are in some cases added to the alloy in the form of chromium carbide particles, and therefore the proportion of metallic chromium is low. In addition, corresponding application processes, for example kinetic cold spraying, are described, but these are not suitable for all applications.
It is nevertheless advantageous for improving the sulfidation resistance, however, to increase the proportion of metallic chromium in an aluminum-rich MCrAlY coating, in order both to achieve a good oxidation resistance and to improve the sulfidation resistance by virtue of the high aluminum proportion.
It would therefore be advantageous to be able to provide a high-temperature protective coating for metallic components, in particular components of turbomachines which are subjected to thermal loading, and also a process for producing the coating, wherein the coating makes it possible to achieve both a good sulfidation resistance and a good oxidation resistance while achieving or retaining required mechanical properties of the coating and of the coated component, and wherein it should be possible for the process to be carried out easily and reliably.